There are various processes known in the art for the recovery of aromatic hydrocarbons from hydrocarbon mixtures. In West German Off. No. 1,568,940, a typical recovery process is disclosed. Such processes have been employed in various large-scale technical projects, and have been successful. Nonetheless, it has been demonstrated that in the working up of certain entry products, such as a crude benzene fraction obtained from pyrolysis benzene, in spite of proper maintenance procedures, fluctuations still occur in the yield of the aromatic hydrocarbon, as well as in the purity thereof. No plausible explanation has been provided.
Whether or not the fluctuations in the product yield or purity have been relatively small, such a problem still represents a significant drawback for any large-scale operation. Not only is the purity of the product open to question but also the yield of aromatic hydrocarbon and/or the energy consumption of the process must be considered.
Thus, for example, where a crude benzene fraction obtained from pyrolysis benzene is worked-up for benzene recovery, not only does the non-aromatic hydrocarbon content of the benzene product fluctuate, but furthermore the non-aromatic hydrocarbon fraction separated from the benzene still contains a significant benzene content. Simultaneously, temperature fluctuations occur in the regulating plates of an extractive distillation column.